Exemplary embodiments of the present invention relate to an electrostatic discharge (ESD) protection circuit, and more particularly, to an ESD protection circuit which is capable of protecting an input/output driver from ESD.
Reliability of semiconductor chips may deteriorate due to the ESD. The ESD may be generated when semiconductor chips are treated or mounted on systems, and such ESD damages the semiconductor chips. Therefore, the ESD protection circuits are arranged in a peripheral region of a semiconductor device in order to protect the semiconductor device from ESD. For example, ESD protection circuits are arranged around data input/output pads of a semiconductor device.
FIG. 1 is an exemplary diagram of an ESD protection circuit used in a known semiconductor memory device. In FIG. 1, the ESD protection circuit is coupled to a data input/output pad.
Referring to FIG. 1, the ESD protection circuit used in the known semiconductor memory device includes a pull-up driver P1 and a pull-down driver N2 as an output driver. The pull-up driver P1 and the pull-down driver N2 are coupled to a data input/output (DQ) pad 10. Specifically, the pull-up driver P1 and the pull-down driver N2 are coupled in series between a power supply voltage (VDD) terminal VDDQ and a ground voltage (VSS) terminal VSSQ. A pull-up resistor R2 is coupled between the DQ pad 10 and the pull-up driver P1, and a pull-down resistor R3 is coupled between the DQ pad 10 and the pull-down driver N2. The pull-up driver P1 and the pull-down driver N2 may be selectively driven by pre-drivers 20 and 30, respectively.
The ESD protection circuit used in the known semiconductor memory device further comprises an ESD protection unit 40 and a power clamp unit 50. The ESD protection unit 40 provides a discharge path of static electricity applied from the outside through the DQ pad 10. The power clamp unit 50 clamps the static electricity applied through the ESD protection unit 40.
The ESD protection unit 40 includes first and second diodes D1 and D2 coupled in series between the power supply voltage terminal VDDQ and the ground voltage terminal VSSQ. The first diode D1 receives positive (+) static electricity greater than a power supply voltage (VDD) to discharge it to the power supply voltage terminal VDDQ, or discharge it to the ground voltage terminal VSSQ through the power clamp unit 50. The second diode D2 receives negative (−) static electricity lower than a ground voltage (VSS) to discharge it to the ground voltage terminal VSSQ, or discharge it to the power supply voltage terminal VDDQ through the power clamp unit 50.
The power clamp unit 50 includes an NMOS transistor N1, a capacitor C1 and a resistor R1. The NMOS transistor N1 is coupled between the power supply voltage terminal VDDQ and the ground voltage terminal VSSQ. The capacitor C1 is coupled between the power supply voltage terminal VDDQ and a gate of the NMOS transistor N1, and the resistor R1 is coupled between the gate of the NMOS transistor N1 and the ground voltage terminal VSSQ.
When the pre-driver 30 is driven, the known ESD protection circuit configured as above pulls down a voltage of an output node through the pull-down driver N2. On the other hand, when the pre-driver 20 is driven, the known ESD protection circuit pulls up the voltage of the output node through the pull-up driver P1. When the pull-up/pull-down operations are performed, the pull-up and pull-down resistors R2 and R3 affects a linearity of a pull-down current and a pull-up current with respect to a voltage applied to the DQ pad 10.
That is, the pull-up and pull-down resistors R2 and R3 serve to interrupt an ESD voltage and an ESD current. However, the pull-up and pull-down resistors R2 and R3 may degrade the I/O buffer interface specification (IBIS) characteristic of an output driver. In particular, since a low-power semiconductor lowers an operating voltage and the pull-up and pull-down resistors R2 and R3 serve to attenuate an output voltage and an output current, the slopes of the linear and saturation regions of the output driver are reduced, resulting in degradation of IBIS characteristic.